The present invention relates to fiber reinforced composites. More particularly, it relates to alternating layers of fibrous structures all embedded in thermoplastic resin.
Thermosetting resins as well as thermoplastic resins are used in forming fiber reinforced composites.
Thermosetting polymer matrices require a substantial time to harden under heat and pressure and so are not suitable for production of parts at high speeds. The fiber/matrix materials or so-called prepreg materials must be refrigerated to extend their shelf life. Furthermore, incorrectly-formed parts or trimmed excess cannot be recovered and re-used On the other hand, thermoplastic polymer matrices are potentially suitable for high-speed production of parts because they can be preheated to forming temperature and pressed only long enough to consolidate the materials and cool the matrix to a temperature at which the part may be removed from the mold without distorting. In addition, the cost of waste is greatly reduced because incorrectly-formed parts may be re-shaped, and scrap may be recovered and re-used.
However, thermoplastic matrices require dealing with higher temperatures and higher viscosities as compared to composites formed with fiber reinforced thermoset resins. Because of the high temperatures and high viscosities involved, thermoplastic resin composites when subject to compression molding suffer from distortion due to fiber movement and "fiber washing" under pressure This results in non-uniform thickness of the product formed during molding with attendant problems associated with such non-uniformity, such as poor mechanical properties.